into a clade descended from a common segmented ancestor. Confocal microscopy and modern molecular biology techniques While each advance in modern molecular biology has shaken the phylogenetic tree of Bilateria, advances in molecular biology techniques led to further data supporting the Articulata hypothesis but also led to the development of conflicting theories. Advances in confocal microscopy technology led to the discovery of embryonic cleavage patterns, which differs between the annelids and arthropods. Annelids show spiral cleavage, meaning that each embryonic cleavage occurs at progressive 90-degree angles with respect to the animal–vegetal axis. Arthropods, on the other hand, display a heterogeneous mix of embryonic cleavage patterns including spiral-like cleavage and radial cleavage patterns. This led researchers to two theories: The first was that the arthropods lineage must have lost the ability to spiral cleave since differentiating from the last common ancestor between annelids and arthropods. The second is that this showed similarities between annelids and mollusks who also spirally cleaves but lacks that the segmented body plan. This was not the only interpretation of this data but other hypotheses were seen to have less data or merit. Other studies such as those looking a neural patterns within the Articulata clade showed mixed patterns and thus mixed results. DNA sequencing and genomics The advancements in DNA sequencing techniques and the development of phylogenetic analysis algorithms led to the splitting of the Articulata clade. Original phylogenetic studies on the sequences of 18S and 28S ribosomal DNA sequence led to the suggestions that the annelids and arthropods had evolutionarily diverged much earlier than was previously thought but such limited genetic studies led to limited and often mixed results. As more genes were added to the studies, it became apparent that arthropods were genetically closer to nematodes and other molting organisms whereas the annelids were closer evolutionary to mollusks. This Ecdysozoa hypothesis is generally accepted today as the best supported evolutionary hypothesis for annelids and arthropods. See also Proarticulata References Phylogenetics